A combustion portion of a can annular gas turbine generally includes a plurality of combustors that are arranged in an annular array around a compressor discharge casing. Pressurized air flows from a compressor to the compressor discharge casing and is routed to each combustor. Fuel is mixed with the pressurized air in each combustor to form a combustible mixture within a primary combustion zone of the combustor. The combustible mixture is burned to produce hot combustion gases having a high pressure and high velocity. The combustion gases are routed towards an inlet of a turbine of the gas turbine through a hot gas path that is at least partially defined by one or more hot gas path ducts such as a combustion liner and/or a transition duct. Thermal and kinetic energy is transferred from the combustion gases to the turbine to cause the turbine to rotate, thereby producing mechanical work. For example, the turbine may be coupled to a shaft that drives a generator to produce electricity.
The hot combustion gases flowing through the ducts) subjects those components to high temperatures and thermal stresses. Hot spots or areas of high thermal stress have been shown to develop within certain areas of the duct due in part to separation of the combustion gases from an inner or hot side surface of the duct. There are certain respective cross sectional flow areas of a duct between a forward or inlet end and an aft or outlet end of the duct. Typically, the cross sectional flow area of the duct will converge or decrease continuously between the forward end and the aft end. Traditionally, this was done to prevent separation between the hot combustion gases and the inner surface of the duct, thereby reducing the thermal stresses within the duct.
Although this design is generally effective for reducing hot spots within a hot gas path duct of a combustor having a single combustion zone, it is less effective for a combustor that includes a secondary combustion zone that is downstream from the primary combustion zone such as a combustor that incorporates late lean fuel injection technology. In particular, a combustor that incorporates late lean fuel injection technology requires additional pressurized air to be injected in to the hot gas path downstream from the primary combustion zone to support combustion in the secondary combustion zone. Injection of the pressurized air results in increased mass flow within the duct at and downstream from the injection point which results in increased velocity of the combustion gases, thereby resulting in increased heat transfer coefficients on the inner or hot side of the duct. Therefore, an improved hot gas path duct or liner for routing the hot combustion gases from the combustor to the inlet of the turbine that incorporates late lean fuel injection would be useful.